Orogenic Gold in Transpression and Transtension Zones: Field and Remote Sensing Studies of the Barramiya–Mueilha Sector, Egypt

Multi-sensor satellite imagery data promote fast, cost-efficient regional geological mapping that constantly forms a criterion for successful gold exploration programs in harsh and inaccessible regions. The Barramiya–Mueilha sector in the Central Eastern Desert of Egypt contains several occurrences of shear/fault-associated gold-bearing quartz veins with consistently simple mineralogy and narrow hydrothermal alteration haloes. Gold-quartz veins and zones of carbonate alteration and listvenitization are widespread along the ENE–WSW Barramiya–Um Salatit and Dungash–Mueilha shear belts. These belts are characterized by heterogeneous shear fabrics and asymmetrical or overturned folds. Sentinel-1, Phased Array type L-band Synthetic Aperture Radar (PALSAR), Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER), and Sentinel-2 are used herein to explicate the regional structural control of gold mineralization in the Barramiya–Mueilha sector. Feature-oriented Principal Components Selection (FPCS) applied to polarized backscatter ratio images of Sentinel-1 and PALSAR datasets show appreciable capability in tracing along the strike of regional structures and identification of potential dilation loci. The principal component analysis (PCA), band combination and band ratioing techniques are applied to the multispectral ASTER and Sentinel-2 datasets for lithological and hydrothermal alteration mapping. Ophiolites, island arc rocks, and Fe-oxides/hydroxides (ferrugination) and carbonate alteration zones are discriminated by using the PCA technique. Results of the band ratioing technique showed gossan, carbonate, and hydroxyl mineral assemblages in ductile shear zones, whereas irregular ferrugination zones are locally identified in the brittle shear zones. Gold occurrences are confined to major zones of fold superimposition and transpression along flexural planes in the foliated ophiolite-island arc belts. In the granitoid-gabbroid terranes, gold-quartz veins are rather controlled by fault and brittle shear zones. The uneven distribution of gold occurrences coupled with the variable recrystallization of the auriferous quartz veins suggests multistage gold mineralization in the area. Analysis of the host structures assessed by the remote sensing results denotes vein formation spanning the time–space from early transpression to late orogen collapse during the protracted tectonic evolution of the belt

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

Atud Bölgesi, Mısır'ın Orta Doğu Çölü'ndeki altın cevherleşmesinin kökeni: Jeolojik, cevher mineralojik ve jeokimyasal yaklaşımlar

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2016Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 2016Bu tez Mısır Doğu Çölü'nün Orta bloğundaki Atud bölgesinde intrüzyonla ilişkili altın yatağının kapsamlı jeolojik, petrografik, mineralojik ve jeokimyasal çalışmaları kapsamaktadır. Tezin amacı, damar tipi mezotermal altın yatağının kökeninin ve onun Doğu Afrika'daki Arap Nubian Kalkanı'nın tektonik gelişimi ile ilişkisinin daha iyi anlaşılmasını sağlamaktır. Elektron mikroprob (EMPA) ve duraylı izotop analizleri, altın yatağının durumunu ve uygun jeotermometrelere göre hidrotermal akışkanı belirlemenin yanı sıra cevher sistemlerinin sıcaklığını, kaynağını, gelişimini ve cevher-taşıyan akışkanların doğasını belirlemek için kullanılmıştır. Bir de ASTER görüntü verisi ile de Atud bölgesindeki altın cevherleşmesi ile ilişkili ana alterasyon tipleri betimlenmiş ve tespit edilmiştir. Mısır'ın Orta Doğu Çölü'nde yer alan çalışma alanı (Atud bölgesi) önceden var olan serpantinit ve metatüf kayaçlarının içine sokulan metagabro-diyorit intrüzyonundan oluşur ve olivin gabronoritlerin daha genç intrüzyonu tarafından kesilmektedir. Atud bölgesindeki damar tipi altın yatakları Mısır'ın Orta Doğu Çölü'ndeki Gabal Atud'da oluşmuş metagabro-diyorit kompleks ile ilişkilidir. Talk karbonat, dolomitik mermer ve kalk-silikatik kayaçlar Gabal-Atud civarında bulunan serpantinitlerden türemişlerdir ve çalışma alanında gözlemlenen Pan-Afrikan ofiyolit segmentlerini temsil eder. Metatüfler Gabal Atud etrafında büyük bir alanı kapsamakta olup serpantinitler ile birlikte mostra vermektedirler. Meta-tüfler mikroskopik olarak mafik-lapilli tüfler, ortaç tüfler, meta-çörtler ve kuvars-biyotit şistler olarak tanımlanabilmektedir. Metagabro-diyorit kompleksi ise haritalanmış alanın büyük bir kısmını kapsamakta ve yarı-dairesel bir şekilde Gabal-Atud'un gövdesini oluşturmaktadır. Metagabro-diyorit kompleksinin yaşı 987-830 Ma arasındadır ve Arabo-Nubian kalkanının erken dönem orojenik komplekslerinden biridir. Serpantinitler ve Metatüfler ile intrüzif dokanağı bulunan kayaç daha sonra olivin gabro-norit karakterli bir sokulum tarafından kesilmiştir. Kayaç ayrıca cevherleşmeler içeren oldukça fazla sayıda kuvars damaraları ve dayklar tarafından doğu ve güneydoğu yamaçlarında gözlemlenen Kuzeybatı-Güneydoğu gidişli gevrek-sünek makaslama zonunda kesilmiştir. Düşük derece metamorfizma geçirmiş gabro ve diyorit kayaçları ve bu kayaçların arasındaki zonda gözlemlenen hibrit lökokratik gabro kayaçları çalışma alanında mostra vermektedir. Olivin gabro-norit karakterli küçük intrüzif kütle Gabal-Atud Gabro diyorit kompleksini kesmektedir. Farklı tipteki dayklar bölgedeki temel kayaçları kesmekte olup genellikle daha yaşlı olanlar KKD-GGB ve daha genç olanlar KB-GD gidişlidir. Daha yaşlı dayklar Lamproifirik karakterli olmakla bereaber serpantitleri kesmektedir. Daha genç dayklar ise andezit porfir karakterli veya aplitik dokulu olup gabro-diyorit kompleksini kesmektedir. Bu altın cevherleşmesi kuvars damarları ve KB-GD kırılgan-sünek makaslama zonu boyunca yoğun hidrotermal alterasyon haleleri içerisinde aynı zamanda bunlar arasındaki kontaklar boyunca yer alır. Kuvars damarları, cevherleşmiş griimsiden beyaza eski damar (KB-GD doğrultulu) ve daha genç, cevherleşmemiş süt beyaz damar (KD-GB) olmak üzere iki gelişimi içermektedir. Altınla ilişkili cevher mineralleri; alt kalkopirit, sfalerit, tetrahedrit ile beraber başlıca arsenopirit ve pirit (tip-I ve II), ilk, ikinci (ana cevher) ve üçüncü (süperjen) fazları olmak üzere cevherleşmenin üç fazı boyunca götitle beraber pirotindir. Üç ana yeraltı hidrotermal alterasyon zonları ana Atud bölgesindeki kuvars damarları boyunca gözlenmiştir; zon 1: kuvars-serisit-pirit, zon 2: kuvars-klorit-karbonat ve zon 3: kalsit-albit-klorit. Au, Ag ve Cu konsantrasyonları zondan zona değişmektedir. Zon 1, 2 ve 3 için sırasıyla bu konsantrasyonlar; 25-790 ppb, 0.7-69.6 ppm ve 6-93.8 ppm; 48.6-176.1 ppb, 0.9-12.3 ppm ve 39.6-118.2 ppm; 53.9-155.4 ppb, 0.7-3.4 ppm ve 0.2-79 ppm'dir. Kütle balansı hesaplamaları (GEOISO-Windows programı kullanılarak hesaplanmış) kullanılarak bu farklı üç zondaki hidrotermal alterasyon süreçleri boyunca kimyasal bileşimlerin kütle/hacim kazanımları ve kayıpları çalışılmış, buna göre altının ana cevherleşme zonu ile, aynı zamanda serisit/kaolinit ve muskovit alterasyonlarının da zon 2 ve 3'ten daha çok zon 1 ile yüksek ilişkili olduğu tespit edilmiştir. Bir de bu alterasyon zonlarının NTE paternleri, La, Eu ve K'nın zon (1) ve (2)'de serisit alterasyonu boyunca hidrotermal solüsyondan kayaçlara eklendiğini, zon (3)'te HNTE anomalilerinin klorit ve karbonat alterasyonları boyunca alkalin hidrotermal solüsyonlarındaki bu elemetlerin düşük çözünürlüklerine işaret eden Mg-zenginleşmeleri ile olduğunu önermektedir. Alterasyon minerallerinin mikroprob verileri, tüm analiz edilmiş pulcuklarda serisitin yüksek muskovit bileşenine sahip olduğunu (ortalama XMs= 0.89), yan kayaçlarda fengit içeriğinin %0.10-0.55 olduğunu ve cevherli kuvars damarlarında fengit içeriğinin %0.13-0.29 olduğunu açığa çıkarmıştır. Yan kayaçlar kuvars damarlarından daha yüksek kalsit (CaCO3) içeriklerine ve daha düşük MgCO3 ve FeCO3 içeriklerine sahiptir. Altere yan kayaçlardaki klorit pulcukları pinoklorit ve ripidolitten oluşmuştur, tahmini oluşum sıcaklıkları sırasıyla 289-295°C ve 301-312°C'dir. Albit, zon 3'teki klorit ile beraber oluşmuş daha yüksek albit içeriğine (%95.08-99.20) sahiptir. Cevher minerallerinin mikroprob çalışmaları, altının electrum (52.2-60.7 atom % Au & 36.7-39.1 atom % Ag) olarak sınıflandırıldığını ve ana cevherli kuvars damarları ve altere ana kayaçlar içerisindeki ana cevherleşme fazındaki arsenopirit ve As-taşıyan pirit ile ilişkili olduğunu ortaya koymuştur. Arsenopirit jeotermometresine dayanarak, arsenopiritteki As-içerikleri (29.3-32.7 atom %), ana cevherleşme fazı boyunca ƒS2 ve T sırasıyla,; -10.5 to -5.5 arasında ve 305-450 °C'deki depolanmaya işaret etmektedir. Bu da altının taşındığına, hidrosülfid kompleksleri AuHS° ve Au(HS)-2'nin artan eksikliğinden dolayı çökeldiğine işaret etmektedir. Sülfidlerin δ34S izotopik kompozisyonlarına dayanarak, bunlar magmatik akışkanlardan kaynaklıdır ki burada sülfür ya direkt magmadan ya da magmatik kayaçlardan yeniden taşınmasından kaynaklanmıştır. Diğer bir deyişle, kalsit, δ13C ve δ18O değerleri baz alındığında, değişken metamorfik izler ile karışık başlıca magmatikleri içeren akışkanlardan oluşmuştur. ASTER-görüntü bant oranlaması (BR), bağıl absorpsiyon bant derinliği (RBD), esas bileşen analizi (PCA), yanlış-renk kompoziti (FCC) ve mineral indeksleri, serisit ve arjilik (kaolinit) alterasyonlarının Atud maden bölgesindeki ana alterasyon tipleri olduğunu, kalsit alterasyonunun maden bölgesi etrafında serpantinit ve talk-karbonat ile sınırlı olduğunu önermiştir. Bu çalışmada Atud yatağındaki altın-taşıyan cevherlerin magmatik kaynaklı olduğu, su/kayaç etkileşimleri boyunca çevre intrüzif kayaçlardan çözünerek, sonrasında metamorfik olaylar boyunca yeniden hareketlendiği sonucuna varılmıştır. Bu yüzden Atud altın yatağı intrüzyonla ilişkili altın yatağı olarak sınıflandırılmaktadır, ana intrüzyon, KB-GD makaslama etkileri sonucu olarak taşınan ve depolanan metallerin kaynağı olarak davranmıştır, bu durum ise çalışma alanındaki altın cevherleşmesinin yapısal kontrollü olduğu anlamına gelir.This thesis provides comprehensive geological, petrographical, mineralogical, and geochemical studies of the gold deposit at Atud area at the Central block of the Egyptian Eastern Desert. It aims to provide a better understanding of the genesis of this vein-type mesothermal gold deposit and its relation to the tectonic evolution of the Arabian-Nubian Shield at East Africa. Electron microprobe (EMPA) and stable isotope analyses are also carried on to identify the conditions of the gold deposition and the mineralizing fluid according to the appropriate geothermometers, as well as to determine the temperature of the ore systems and the source, evolution, and nature of the ore-bearing fluids. Moreover, ASTER imagery data are used to delineate and detect the main alteration types associated with the gold mineralization at Atud area. The study area (Atud area) that located in the Central Eastern Desert of Egypt is made up of a gabbro-diorite intrusion emplaced into the pre-existing rocks; serpentinite and metatuffs and is cut by a younger intrusion of olivine gabbronorite. The vein-type gold deposits in the Atud area are related to the metagabbro-diorite complex that occurred in Gabal Atud in the Central Eastern Desert of Egypt. The dispersed talc-carbonate, dolomitic marble and calc-silicate rocks are derivatives of serpentinite around Gabal Atud. They represent the Pan-African dismembered ophiolitic rocks exposed in the study area. Metatuffs cover a vast area of the area around Gabal Atud where they form low-lying outcrops associated with serpentinite rocks. They are microscopically differentiated into different varieties; mafic lapilli metatuffs, intermediate metatuffs, metacherts, and quartz-biotite schists. The metagabbro-diorite complex covers a large proportion of the mapped area and exists as a semicircular body of Gabal Atud. It represents one of the early orogenic gabbro-diorite complexes in the Arabian-Nubian Sheild and its age ranges from 987 to 830 Ma. It had an obvious intrusive contact against serpentinites and metatuffs and later was invaded by olivine gabbronorite. It also was cut by numerous mineralized and barren quartz veins and dikes at its eastern and southeastern slopes, where NW-SE brittle-ductile shear zone cuts through this complex. Slightly metamorphosed gabbro and diorite rocks and hybrid leucocratic gabbro zone in between are exposed at the study area. Olivine gabbronorite forms a small intrusion cutting the gabbro-diorite complex of Gabal Atud. There are different types of dikes cut through the country rocks in the mine area, trend mainly in two directions. The oldest one is NNE-SSW and the youngest is NW-SE. Lamprophyre dikes occupy commonly the old direction (NNE-SSW) and cut through the serpentinite rocks, while porphyritic andesite and aplitic dikes occupy the NW-SE direction and cut through the gabbro-diorite intrusion. This gold mineralization is associated with quartz veins and intense hydrothermal alteration haloes along the NW-SE brittle-ductile shear zone, as well as along the contacts between them. Two generations of quartz veins include the mineralized grayish-to-white color old vein (trending NW-SE), and the younger, non-mineralized milky white vein (trending NE-SW). The ore minerals associated with gold are essentially arsenopyrite and pyrite (type-I and II), with subordinate chalcopyrite, sphalerite, tetrahedrite, and pyrrhotite with goethite forming in three stages of mineralization: first, second (main ore), and third (supergene) stages. Three main subsurface hydrothermal alteration zones were determined around the quartz veins in the main Atud area: zone 1: sericitic alteration (mainly sericite/muscovite and kaolinite with subordinate quartz and pyrite), zone 2: phyllic alterations (mainly quartz and sericite with pyrite and subordinate albite quartz-chlorite-carbonate), and zone 3: carbonate propylitic alterations (mainly carbonate (ankerite/calcite) and chlorite (chamosite/clinochlore) with albite and arsenopyrite). Concentrations of Au, Ag, and Cu are different from zone to zone by having 25-790 ppb, 0.7-69.6 ppm, and 6-93.8 ppm; 48.6-176.1 ppb, 0.9-12.3 ppm, and 39.6-118.2 ppm; and 53.9-155.4 ppb, 0.7-3.4 ppm, and 0.2-79 ppm for zone 1, 2, and 3, respectively. By using the mass balance calculations (calculated using the GEOISO-Windows program), the mass/volume gains and losses of the chemical components during the hydrothermal alteration processes in these different zones were studied revealing that the gold to be highly associated with the main mineralized zone as well as sericite/kaolinite and muscovite alterations in zone 1 more than in zones 2 and 3. Also, the REE pattern of these alteration zones suggested that La, Eu, and K added to the rocks from hydrothermal solution during the sericitization in zones (1) and (2), while in zone (3) HREE anomalies are with Mg-enrichments indicating low solubility of these elements in alkaline hydrothermal solutions during chloritization and carbonatization. Microprobe data of the alteration minerals revealed that the sericite had a higher muscovite component in all analyzed flakes (average XMs= 0.89), with 0.10%-0.55% phengite content in wall rocks and 0.13%-0.29% phengite content in mineralized quartz veins. The wall rocks had higher calcite (CaCO3) contents and lower MgCO3 and FeCO3 contents than the quartz veins. The chlorite flakes in the altered wall rocks were composed of pycnochlorite and ripidolite, with estimated formation temperatures of 289-295°C and 301-312°C, respectively. Albite had higher albite content (95.08%-99.20%) which occurs with chlorite in zone 3. While the microprobe studies of ore minerals reveal that gold can be classified as electrum (52.2-60.7 atom % Au & 36.7-39.1 atom % Ag) and is associated with arsenopyrite and As-bearing pyrite in the main mineralization phase within the main mineralized quartz veins and altered host rocks. Based on the arsenopyrite geothermometer, As-contents (29.3-32.7 atom %) in arsenopyrite point to deposition in the ƒS2 and T ranges of -10.5 to -5.5 and 305-450 °C, respectively during the main mineralizing stage. This indicates that the gold is transported and precipitated due to increasing lack of the hydrosulphide complexes AuHS° and Au(HS)-2. Based on the δ34S isotopic compositions of the sulfides (2.8 – 9.5 ‰ from mineralized quartz veins and 0.7 – 7.8 ‰ from the altered host rocks), they are originated from magmatic fluids in which the sulfur is sourced either directly from magma or remobilized from the magmatic rocks. On the other hand, calcite formed from fluids having magmatic mixed with metamorphic signatures based on its δ13C (-10.6 to -8.0 ‰VPDB) and δ18O (13.1 to 14.5 ‰SMOW) values. ASTER-imagery band rationing (BR), relative absorption band depth (RBD), principal component analysis (PCA), false-color composite (FCC), and mineral indices suggest the sericitic and argillic (kaolinite) alterations are the main alteration types detected at the main Atud mine area, while the calcite alteration is confined to the serpentinite and talc-carbonate around the mine area. This work concluded that the gold-bearing ores at Atud deposit have magmatic sources leaching from the country intrusive rocks during water/rock interactions then remobilized during a metamorphic event. Therefore, the Atud gold deposit is classified as an intrusion-related gold deposit, in which the host intrusion acted as the source of metals, which were later mobilized and deposited as a result of NW-SE shearing. This also refers to the gold mineralization at the study area was structurally controlled.DoktoraPh.D

Geochemical characteristics of the Pan-African basement rocks at Atud area, Central Eastern Desert, Egypt

Bu çalışmada, Atud bölgesi’ndeki (Mısır'ın Orta Doğu Çölü) Prekambriyen Pan-Afrikan temel kayaçlarının jeolojik yerleşimlerini, jeokimyasal özelliklerini, saha ilişkilerini, tektonik yerleşimlerini ve petrojenezlerini belirlemek için petrografik ve jeokimyasal özellikleri ortaya konulmuştur. Atud Bölgesi’nde serpantinitler, bunların türevleri ve metatüfler, metagabro-diyorit kompleksi tarafından kesilmektedir. Metagabro-diyorit kompleksi ise olivin gabronoritik kayaçlar tarafından kesilmektedir. Serpantinitler, talk-karbonat ve kalk-silikat kayaçları metamorfik peridotitler olarak adlandırılmıştır. Nadir toprak elementleri (NTE) davranışları, HNTE ve pozitif Eu-anomalisi ile ANTE zenginleşmeleri ile karakterize edilir. Bu durum, hidrotermal akışkanların plajiyoklaz çözünmesi ve/veya sirkülasyonu ile doğada meydana gelen okyanus serpantinleşmesine işaret etmektedir. Metatüfler çoğunlukla en yüksek K/Rb oranına sahip olan bazik ile ortaç dereceli magma odalarından türetilmiştir. NTE paternleri, HNTE açısından zenginleşmiş, ANTE'den yoksun ve negatif Eu anomalilerine sahip genelde toleyitik ve kalk-alkalin kayaçlarla okyanus ada yayının metasedimentlerine benzemektedir. Ayrıca, dalma-batma zonu boyunca manto kaynağına eklenen bileşenler tarafından kirlenmiş bir magmadan kaynak kayaçlarının oluştuğunu ifade etmektedir, yani negatif Eu-, Sr- ve Zr- anomalileri göstermektedir. Metagabro-diyorit kompleksi kayaçlarının sırasıyla kalk-alkalin gabro ve gabro/diyorit ve diyorit ve gabro/diyorit olduğunu ortaya koymaktadır. Bu kayaçlar, sırasıyla metagabrolar ve diyoritler için klinopiroksen ve amfibol fraksiyonasyonuna işaret eden ada yayı ortamlarında meydana gelen kalk-alkali bazalt (CAB) ile karşılaştırılabilir. Öte yandan, olivin gabronorit kayaçları, K toleyitik magmatik afinitelere sahip gabroik kayaçlar olarak sınıflandırılır. NTE paternleri, HNTE ile zenginleşmeyi ve pozitif Eu-, Th-, Pb-, Sr- ve Zr-anomalileri ve plajiyoklaz ve olivin düşük basınçlı fraksiyonasyonunu ima eden negatif P- ve Ti-anomalileri ile ANTE açısından tüketilmeyi ortaya koymaktadır.This paper reports the geochemical characteristics of the Precambrian Pan-African basement rocks of the Atud area (Central Eastern Desert of Egypt) to clarify their geological setting, field relationships, and petrographic and geochemical characteristics to define their tectonic setting and petrogenesis. The Atud area is made up of serpertinites and their derivatives and metatuffs that intruded by metagabbro-diorite complex and later intruded by olivine gabbronorite rocks. The serpentinites, talc-carbonate, and calc-silicate rocks refer to be metamorphic peridotites. Their rare earth elements (REE) behavior is characterized by enrichment in LREE and flat HREE with positive Eu-anomaly. This suggests to the oceanic serpentinization in nature occurred with the plagioclase circulation/dissolution of the hydrothermal fluids. The metatuffs were mostly derived from basic to intermediate magmatic suites pointing to have highest K/Rb ratio. They are, therefore, similar to the metasediments of the oceanic island arc having tholeiitic to calc-alkaline affinities and negative Eu-anomalies, HREE-depleted, and LREE-enriched patterns. Moreover, their source rocks originated from a magma contaminated by components added to the mantle source along the subduction zone that is back to their negative Eu-, Sr-, and Zr- anomalies. The metagabbro-diorite complex rocks show calc-alkaline gabbro and gabbro/diorite and diorite and gabbro/diorite, respectively. They are comparable with the calc-alkaline basalt (CAB) occurred in island arc setting indicating clinopyroxene and amphibole fractionation for the metagabbros and diorites, respectively. On the other hand, the olivine gabbronorite rocks are low-K tholeiitic gabbroic rocks having enrichment in the LREE and flat HREE. In addition, their REE pattern show negative anomalies of P and Ti and positive anomalies of Eu, Pb, Sr, Th, and Zr. It concluded that the gabbronorite rocks display low-pressure fractionation of olivine and plagioclase

The nature of gold-bearing fluids in Atud gold deposit, Central Eastern Desert, Egypt

<p>Electron microprobe analyses of gold and associated ore minerals as well as stable isotope analyses of sulphide and carbonate minerals were performed in order to determine the metal and fluid sources and temperature of the mineralizing systems to better understand the genesis of the Atud gold deposit hosted in the metagabbro–diorite complex of Gabal Atud (Central Eastern Desert, Egypt). The gold can be classified as electrum (63.6–74.3 wt.% Au and 24.6–26.6 wt.% Ag) and is associated with arsenopyrite and As-bearing pyrite in the main mineralization (gold-sulphides) phase within the main mineralized quartz veins and altered host rocks. Based on the arsenopyrite geothermometer, As-contents (29.3–32.7 atom%) in arsenopyrite point to deposition in the Log ƒ_S2 and T ranges of −10.5 to −5.5 and 305–450°C, respectively, during the main mineralizing phase. Based on the <i>δ</i>³⁴S isotopic compositions of the sulphides, they are originated from magmatic fluids in which the sulphur is either sourced directly from magma or remobilized from the magmatic rocks (gabbroic rocks). On the other hand, calcite formed from fluids having mainly magmatic mixed with variable metamorphic signatures based on its <i>δ</i>¹³C and <i>δ</i>¹⁸O values. This work concluded that the gold-bearing ores at Atud deposit have magmatic sources leaching from the country intrusive rocks during water/rock interactions then remobilized during a metamorphic event. Therefore, the Atud gold deposit is classified as an intrusion-related gold deposit, in which the gabbro–diorite host intrusion acted as the source of metals which were mobilized and deposited as a result of the effects of NW–SE shearing.</p

Geochemistry of Hydrothermal Alteration Associated with Cenozoic Intrusion-Hosted Cu-Pb-Zn Mineralization at Tavşanlı Area, Kütahya, NW Turkey

The Miocene magmatic intrusion in the Tavşanlı zone of the Kütahya-Bolkardağ Belt (KBB) in the northwestern region of Turkey is represented by the Eğrigöz granitoids. This paper studies the petrology and geochemistry of hydrothermal alterations associated with the vein-type Cu-Pb-Zn mineralization hosted by this pluton, focusing on the determination of the mass gains and losses of chemical components, which reflect the chemical exchanges between the host rocks and hydrothermal fluids. Vein-type Cu-Pb-Zn mineralization is closely associated with intense hydrothermal alterations within the brecciation, quartz stockwork veining, and brittle fracture zones that are controlled by NW-SE trending faults cutting through the Eğrigöz granitoids. Paragenetic relationships reveal three stages of mineralization: pre-ore, ore, and supergene. The ore mineralogy typically includes hypogene chalcopyrite, sphalerite, galena, and pyrite, with locally supergene covellite, malachite, and azurite. Wall-rock hypogene hydrothermal alterations include pervasive silicification, sulfidation, sericitization, and selective carbonatization and albitization. These are distributed in three main alteration zones (zone 1: silicified/iron carbonatized alterations ± albite, zone 2: argillic-silicic alterations, and zone 3: phyllic alterations). Based on the gains and losses of mass and volume (calculated by the GEOISO-Windows™ program), zone 1 has a higher mass and volume gain than zones 2 and 3. Non-systematic zonal distributions of alterations are observed in which the silicic-carbonate alterations +/− albitization appeared in zone 1 in the center and the phyllic-argillic alterations appeared in zones 2 and 3, with an increase in base metals (Cu-Pb-Zn) in the zone from Cu, Cu-Pb, to Cu-Pb-Zn moving outwards

Evolution of the Tepeoba porphyry-skarn Cu-Mo-Au deposit, NW Turkey: New mineralogical and geochemical findings

This study recently investigates the evolution of the Tepeoba porphyry Cu-Mo-Au deposit (Cu similar to 3 wt%, Mo similar to 0.16 wt%, Au similar to 10 ppm) with associated skarn prospects in the Biga Peninsula (NW Turkey) using the geochemical and mineralogical data. Ore-related alteration types which include biotite (+/- muscovite)-K-feldspar at the center of the mineralization zone, actinolite-albite alteration, and outer chlorite-epidote-calcite mineral facies, are observed in the Tepeoba mine area along the southern contact between the Karakaya Complex (mainly hornfels at the mine area) and porphyry Eybek intrusion. Porphyry style alteration pattern has been detected recognized in the porphyritic microgranite host rock. On the other hand, the calcareous and carbonate as well as the mineralized hornfels refer to the skarn style alteration pattern associated with a porphyritic felsic stock. Sulfide-rich stockwork and mineralized brittle brecciated, and fracture zones are associated with these hydrothermally altered wallrocks. Ore mineralogy includes chalcopyrite, molybdenite, pyrrhotite, pyrite, subordinate cubanite and native gold. These minerals are replaced by marcasite, hematite, and goethite in the oxidized cap rocks. EPMA data of the alteration and sulfide minerals revealed that Cu-, Fe-, Mo-sulfides partially replace biotite +/- muscovite-K-feldspar/actinolite-albite and chlorite-epidote-calcite alteration facies. The estimated ore formation conditions returned wide range of temperatures of 546-471 degrees C (biotite thermometry) to 340-264 degrees C (chlorite thermometry), at which sulfides had most likely precipitated while the oxygen fugacity of the magmatic-hydrothermal ore fluids was gradually lowered and developed during the stage of retrograde metasomatic reactions. Chalcopyrite and cubanite was likely to have formed via un-mixing of intermediate solid solution (iss) under oxidizing hydrothermal conditions. Under these conditions, thiosulfide complexes could have been responsible for the transport and deposition of gold. This also refers to native gold, which could have been liberated from sulfide ores (i.e., pyrite) in the oxidation zone due to the processes of supergene enrichment